This invention relates to an apparatus for pretreating biological specimens, such as pieces of tissue, with a variety of reagents and finally embedding them in paraffin or like substance, thereby preparing blocks to be microtomed into thin slices, known micro-logically as sections, for microscopical study.
Of several known types of microscope slide commonly used today, sections are perhaps the best suited for detailed study of the tissues or cells of organic structures. Direct hand slicing is possible for some structures. But most biological specimens do not lend themselves to such treatment but must be impregnated with, and embedded in, a substance that sections well. The preparation of paraffin blocks requires such pretreatments of the specimens as degreasing, dehydration, and fixation of tissue by immersion in alcohol, formalin, and xylene, among other reagents.
Apparatus has been suggested and used for pretreating biological specimens in various ways and embedding the pretreated specimens in paraffin, all in a single vessel. The apparatus comprises a required number of reagent vessels containing molten paraffin and other reagents. A rotary selector valve coacts with a gate valve to communicate the reagent vessels with the single processing vessel in a prescribed sequence, the latter vessel having biological specimens placed therein. The processing vessel draws the reagents in from the successive reagent vessels by being evacuated with an air pump and discharges them either by admitting atmospheric air or by being pressurized with the pump.
The known apparatus has several drawbacks. The first of these concerns the supply and discharge of the reagents to and from the processing vessel. For reagent supply the usual practice has been to maintain the processing vessel in partial vacuum for a length of time required for the complete contents of each reagent vessel to flow into the processing vessel, plus some extra period. This practice is objectionable because the reagent vessels may contain less than required amounts of reagents. The prior art apparatus has no means for sensing the undersupply of the reagents, possibly resulting in the exposure of the specimens in the processing vessel to air for a prolonged length of time and so making them unsuitable for microscopical investigation.
For reagent discharge, too, the conventional practice has been to deliver air under pressure into the processing vessel for a period of time required for the full withdrawal of the reagent therefrom, plus some added time. During this additional period, then, the pressurized air flows into the reagent vessel to which the reagent has been recovered from the processing vessel. The influx of the pressurized air into the filled reagent vessel causes the bubbling of the recovered reagent and the consequent evaporation of the solution and the liberation of noxious gases.
It must also be taken into consideration that the extra periods during which the processing vessel is held evacuated and pressurized for reagent supply and discharge sum up to a considerable length of time since the reagent vessesl number as many as fourteen or so. Such waste of time should of course be avoided.
Another drawback in the prior art is that, as far as the applicant is aware, no measure has been taken against pollution of the working environment. The reagents for the processing of organic specimens include chloroform, xylene, alcohol, etc., which emit gases that are toxic when inhaled. The apparatus is usually installed in a closed space and operates for an extended period of time, during which the concentrations of the noted gases may increase to fatal degrees.
Also, in the known apparatus, trouble has been liable to occur from the directional control valve for selectively communicating the processing vessel with the pump and with atmosphere. In the event of the malfunctioning of this valve the processing vessel may fail to discharge a reagent and may still be charged with another. Overflowing from the vessel, the blended reagents will then enter and destroy the pump. Moreover, if a trouble occurs to the rotary selector valve, a reagent drained from the processing vessel may be directed into a wrong reagent vessel thereby causing overflow therefrom. The rotary valve as heretofore constructed has been unsatisfactory in respects of durability and resistance to heat and chemicals.